Method of operating honing feed system having full control of feed force, rate, and position

Abstract

The feed system for a honing machine provides a capability to dynamically correct in real time errors in bore size inferred arising from variations in feed force, and a method of operation of the same. The system allows a user to select between rate and force controlled honing modes, which provides one or more of the advantages of both modes. The system provides capabilities for automatic rapid automatic bore wall detection, compensation for elasticity of elements of the feed system and honing tool, and automatic tool protection. The system is automatically operable using feed force, feed rate and positional information for honing a work piece to one or more target parameters, such as one or more in-process sizes and a final size.

1. A method of honing a surface of a bore of a workpiece, comprising steps of:
 providing a honing tool supported on a spindle for rotation about an axis through the tool and for axial stroking movement, the honing tool having at least one radially expandable honing element; 
 providing a feed system in connection with the honing tool, including a movable feed element automatically controllably operable for applying a feed force against the honing tool for radially expanding the at least one honing element; 
 providing a control operable for automatically controlling operation of the feed system; 
 providing a stroking system operable for axially stroking the honing tool along the axis; 
 providing a drive for rotating the honing tool about the axis; 
 providing a device for determining information representative of a feed force applied against the honing tool by the feed element and outputting a signal representative thereof to the control; 
 providing a device for determining information representative of a position of the feed element and outputting a signal representative thereof to the control; 
 automatically operating the feed system to move the feed element to radially expand the at least one honing element unrestrained by a surface of a bore, and determining information representative of a baseline feed force required for the expansion; 
 automatically operating the feed system to move the feed element at a first feed rate to radially expand the at least one honing element within the bore of the workpiece without rotating or stroking the honing tool, so as to initially contact the surface of the bore to cause a responsive increase in the feed force to a level greater than the baseline feed force serving as an indicator of the contact; then 
 automatically radially retracting the at least one honing element to reduce the feed force; and then 
 commencing rotation and stroking of the honing tool while operating the feed system at a second feed rate slower than the first feed rate to radially expand the at least one honing element for contacting and honing the surface of the bore. 
 
   
   
     2. The method of  claim 1 , comprising additional steps of automatically determining a value representative of the diameter of the bore as a function of a position of the feed element at a time of the contact with the surface of the bore;
 automatically comparing the value representative of the diameter of the bore with a known value, and if greater than the known value, then signaling that the bore is defective. 
 
   
   
     3. The method of  claim 1 , wherein the step of determining information representative of a baseline feed force required for the expansion comprises determining a range of values for the feed force. 
   
   
     4. The method of  claim 1 , wherein the honing element comprises a radially expandable sleeve. 
   
   
     5. The method of  claim 1 , comprising additional steps of:
 automatically honing at least two bores to a predetermined enlarged diameter, including for each of the bores performing the step of operating the feed system to move the feed element to radially expand the at least one honing element so as to contact the surface of the bore, and determining a value representative of the diameter of the bore as a function of a position of the feed element at a time of the contact; and 
 determining a value representative of wear of the at least one honing element as a function of the values representative of the diameters of the bores at the contact and positions of the feed element when the bores are honed to the enlarged diameter. 
 
   
   
     6. The method of  claim 5 , comprising a further step of automatically calculating a cost of honing the bores at least in part as a function of the value representative of wear. 
   
   
     7. The method of  claim 6 , wherein the step of automatically calculating a cost of honing includes calculating the cost additionally as a function of a value representative of a cost of operating the honing machine for honing the bores. 
   
   
     8. The method of  claim 6 , wherein the step of automatically honing at least two bores comprises automatically selecting different honing parameters for honing the bores to the predetermined enlarged diameter, respectively, and honing the bores to the enlarged diameter using the different honing parameters, and the step of automatically calculating a cost of honing the bores includes calculating a cost for honing each of the two bores. 
   
   
     9. The method of  claim 1 , wherein the second feed rate comprises a substantially constant rate. 
   
   
     10. The method of  claim 1 , wherein the second feed rate is selected for controlling the feed force at a substantially constant level. 
   
   
     11. The method of  claim 1 , wherein the second feed rate is selected for controlling the feed force at varying levels following a predetermined profile. 
   
   
     12. The method of  claim 1 , wherein the device for determining information representative of the feed force applied against the honing tool by the feed element comprises a load cell disposed between the feed element and the honing tool. 
   
   
     13. The method of  claim 1 , wherein the device for determining information representative of the position of the feed element comprises an encoder in connection with the feed element. 
   
   
     14. The method of  claim 1 , wherein the second feed rate comprises variable levels following a predetermined profile. 
   
   
     15. The method of  claim 14 , wherein the second feed rate varies at levels following a profile which is determined at least in part as a function of the information representative of the feed force.